1. The Field of the Invention
This invention relates to apparatus, methods, and systems for tuning optical beams, and in particular, to methods and systems for generating comparatively high pulse energies with an ability to change wavelengths.
2. The Background Art
Eye-safe lasers, having wavelengths in the 1.4 to 2.1 μm range, are used in a wide variety of systems for remote sensing and other applications. Remote sensing instruments use LIDAR (Light Detection and Ranging) techniques for chemical determination, aerosol characterization, and range measurements. For these remote sensing techniques, in which humans may find themselves in the path of the laser, it is important for the laser pulses to be in the eye-safe regime.
The utility of eye-safe lasers is not limited to remote sensing applications. Eye-safe lasers are used in telecommunication equipment and medical systems and find applications in velocimetry techniques and materials processing.
Optical parametric oscillators (OPO) are a type of system that can be used to generate eye-safe laser pulses. An optical parametric oscillator is a light source similar to a laser, but based on optical gain from parametric amplification in a nonlinear crystal rather than stimulated emission. Parametric amplification is a phenomenon where a signal wave can be amplified using a χ2 or χ3 optical nonlinearity in a crystal medium together with a pump wave. For an OPO system, a χ2 nonlinearity in the crystal is required to produce frequency conversions.
Optical parametric oscillators (OPO) are utilized in spectroscopy and other scientific applications where it is desired to cover very broad spectral regions and to deliver outputs with narrow linewidths and high power. Typical OPO frequency tuning requires the mechanical movement of the crystal. Changing the angle of the crystal relative to the pump beam results in a different optical path through the crystal. Thus, different wavelength signal and idler beams are produced.
This method for OPO frequency tuning may rely on changing the angle of the crystal or the angle of incidence of the pump beam. The latter can be accomplished by physically moving the pump laser or adjusting the optical components to redirect the pump beam. Mechanical OPO tuning has associated problems encountered with position accuracy, repeatability, and optical alignment inherent in systems with moving parts. Other tuning techniques include changing the temperature or pressure of the crystal or applying a large voltage to the crystal.